Coronary artery disease is the leading cause of morbidity and mortality in the United States and in most developed countries. Atherosclerosis and its complications such as myocardial infarction and stroke, is mainly responsible for coronary artery disease. All together, atherosclerosis accounts for at least forty-three percent of all death in the United States affecting over 60 million people (American Heart Association, 2004).
Advances in basic science indicate coronary artery disease is an inflammatory process, characterized by a long cycle of irritation, injury, healing and re-injury to artery endothelial cells. There is growing evidence that mast cells are found in the various stages of atherosclerosis, coronary inflammation and cardiac ischemia (Libby 2002; Fernex, 1968; Mor and Mekori, 2001; Kelly, Chi, et al., 2000; Sun, Sukhova, et al., 2007; Huang, Pang, et al., 2002). Mast cells, located in connective tissue, play an important role in helping the immune system defend tissues from disease by activating the release of intracellular mediators (degranulation), as well as attracting other key players of the immune defense system to areas of the body where they are needed. In response to vascular injury, cardiac mast cells interact with lipoproteins to deliver lipids to macrophages, and to release a large variety of cytokines that affect smooth muscle cells and T lymphocytes. This process can develop into the more advanced and complex occlusive lesions, termed fibrous plaques. Other pro-inflammatory mediators released by mast cells are histamine, which can constrict the coronaries, and cytokines IL-6 and IFN-gamma, which induce degradation of the extracellular matrix and the death of smooth muscle cells in the wall of the aorta, weakening the walls and allowing it to dilate. Thus, the inflammatory response stimulates endothelial dysfunction causing migration and proliferation of smooth muscle cells that become intermixed in the area of inflammation to form fibrous plaques and complicated lesions.
Disodium cromoglicate, termed “cromolyn,” is the disodium salt of cromoglicic acid. It is used as an anti-inflammatory medication. Cromolyn is described in the literature as a mast cell stabilizer since it works by preventing the release of mediators such as the vasoactive and pro-arrhythmogenic chemical histamine and cytokines from mast cells thus stabilizing inflammatory cells. Prevention of mediator release is thought to result from indirect blockade of the entry of calcium ions into the membrane of sensitized mast cells. Cromolyn has also been shown to inhibit the movement of other inflammatory cells such as neutrophils, eosinophils, and monocytes (8).
Recent studies in mice have demonstrated that systemic mast cell activation during atherogenesis leads to plaque formation (Bot, de Jager, et al., 2007). Furthermore, treatment of the animals with the mast cell stabilizer cromolyn prevented dinitrophenyl-albumin-induced plaque expansion. In another study, cardiac mast cell activation was studied in mice after stress-related coronary inflammation (Huang, Pang, et al., 2003). Activated mast cells were found adjacent to atherosclerotic vessels. In cromolyn treated mice, release of the pro-inflammatory cytokine interleukin-6 (IL-6) present in mast cells, was partially inhibited.
There is growing evidence that activated cardiac mast cells are increased in association with coronary inflammation, myocardial infarction, as well as ischemic cardiomyopathy. Moreover, mast cells can promote the formation of human atherosclerotic lesions by causing endothelial dysfunction of the heart's arteries that lead to plaque buildup. Since cromolyn targets sensitize mast cells, a labeled cromolyn analog potentially could serve as a diagnostic probe for early detection of coronary artery disease.
As can be appreciated, it would be desirable to obtain new imaging agents useful for detecting degenerative diseases in human subjects. In particular, novel imaging probes that associate with markers of inflammation such as mast cells would facilitate the early detection of inflammatory diseases such as atherosclerosis by utilizing sensitive and non-invasive approaches such as PET or MRI imaging. Such new compounds may also provide unexpected therapeutic benefits for treatment of conditions including, but not limited to, inflammation, infection, atherosclerosis and Alzheimer's Disease.